Oligomers of perfluoro(2,2-dimethyl-1,3-dioxole) and their fluorination products

ABSTRACT

Perfluoro(2,2-dimethyl-1,3-dioxole) forms oligomers on standing in the presence of an ether. The preferred ethers are aliphatic and cycloaliphatic, especially tetrahydrofuran. Free radical generators, especially peroxydicarbonates, may be added to the reaction medium. The oligomers have a degree of polymerization of about 2-8. They are useful as lubricants, hydraulic fluids, heat transfer agents, and plasticizers, and as intermediates to oligomeric acid fluorides and acids, which acids are useful surfactants.

This is a division, of application Ser. No. 279,867, filed July 2, 1981,now U.S. Pat. No. 4,409,393.

BACKGROUND OF THE INVENTION

This invention relates to oligomers ofperfluoro(2,2-dimethyl-1,3-dioxole), which are useful as lubricants,hydraulic fluids, heat transfer fluids, and plasticizers, and asintermediates for making certain perfluoroacids and acid fluorides.

U.S. Pat. No. 3,978,030 to Resnick discloses solid polymers ofperfluoro(2,2-dimethyl-1,3-dioxole). The preparation ofperfluoro(2,2-dimethyl-1,3-dioxole), sometimes abbreviated hereafter toPDD, also is described in the above patent. PDD has the followingformula (1) ##STR1##

Solid polymers were obtained on standing at room temperature in a drybox as well as on irradiation with ultraviolet light. No low molecularweight oligomers of PDD have been reported, however.

SUMMARY OF THE INVENTION

There are now provided oligomers of perfluoro(2,2-dimethyl-1,3-dioxole),which form spontaneously when this compound is allowed to stand in thepresence of an ether. There also are provided oligomeric perfluoroacidsand acid fluorides obtained by fluorination with elemental fluorine ofthe above PDD oligomers.

DETAILED DESCRIPTION OF THE INVENTION

The oligomers of the present invention form at temperatures as low as-5° C. or even lower or as high as 70° C. or so. Although theoligomerization is faster at higher temperatures, it is a slow reaction,which may take days, weeks, or months at -5° C. Since PDD boils at 33°C., it is recommended that oligomerization above 60° C. be carried outin pressure equipment.

Aliphatic and cycloaliphatic ethers are preferred because in theirpresence the highest conversions are obtained. Representative etherswhich can be used to make the oligomers of this invention include:methyl, ethyl, propyl and isopropyl, and butyl ethers; tetrahydrofuran,dioxane, and dioxolane; methylal, diethyl acetal, and dimethyl heptal;and polymeric ethers such as polyethylene oxide, polypropylene oxide,and acetals of polyvinyl alcohol. It is not necessary to purify theether to remove ether peroxides which usually are present therein.

The normal way of carrying out this oligomerization is to dissolve PDDin the ether and let the solution stand at the desired temperature for aperiod of at least several hours, then distill off any unchanged PDD andthe ether. The oligomer product is found in the heel (residue) of thedistillation. It has been found practical to also have water present inthe oligomerization medium. The volume of water may thus vary from zeroto about twice the volume of the ether, the latter being about one tothree times the volume of PDD. However, neither the presence of waternor the above-recited volume proportions are critical to the success ofthis invention.

The preferred ether is tetrahydrofuran because in its presence theoligomerization proceeds relatively quickly; it is miscible with water;and it has a low boiling point of 65°-66° C., which permits easy removalby distillation.

It is often advantageous to add an initiator to the reaction. Theinitiator can be any free radical generator known to the art. Many freeradical generators are commercially available. They usually are peroxy,peroxycarbonyl, or azo compounds. The proper choice will depend, amongothers, on the initiator's decomposition temperature at which freeradical generation takes place. The preferred initiators will rapidlygenerate free radicals at about 50°-65° C. Those having lowerdecomposition temperatures may present a safety hazard. The particularclass of initiators preferred in the process of this invention areperoxydicarbonates such as, for example, bis(4-t-butylcyclohexyl)peroxydicarbonate.

This oligomerization reaction being free radical-initiated andterminated, the oligomers will contain groups derived from the freeradical molecule. Aliphatic and cycloaliphatic ethers react readily withPDD, so that at least a portion of all the PDD oligomers formed in thereaction will contain ether residues. The oligomers of this inventioncan be shown by instrumental methods such as infrared and nuclearmagnetic resonance spectroscopy to form chains comprised of PDD unitsjoined through double bonds as shown below in Formula (2). ##STR2##where k is about 1-4 but usually is at least 2. R and R₁ are fragmentsof the radical causing oligomer chain initiation and termination. Eachof R and R₁ can thus be hydrogen or an ether residue; or, it can be agroup derived from any initiator present. The R and R₁ groups do notnecessarily have to be always located at the ends of the oligomermolecule but may be inside the molecule. Thus, when the oligomerizationis carried out in the presence of tetrahydrofuran, oligomers having thefollowing structures (3) and (4) may be formed: ##STR3## where n isabout 2-8 while each of m and p is about 1-4 but usually at least 2, andthe average degree of oligomerization of products (3) and (4) is aboutthe same; so that for the purpose of this disclosure in structures (3)and (4) m+p ≈n.

The upper limit of n in most oligomers will be 4 to 6. At the upper endof the n range, the oligomers will be very viscous liquids orlow-melting noncrystalline solids (waxes) incapable of being pressedinto self-supporting films. Where n is a low number, the oligomer is amobile liquid.

Fluorination of the oligomers of the present invention with elementalfluorine may lead to perfluoroacid fluorides or perfluoroacids. Thus, anoligomer of formula (3), above, gives a product of both fluorination andcleavage, which has the following structure (5). ##STR4## which can bereadily hydrolyzed by a mild base to the corresponding perfluoroacidsalt, e.g., (6) ##STR5## Acids and salts such as 6 are usefulsurfactants for fluoromonomers in emulsion polymerization reactions.Acid fluorides (5) undergo the usual reactions of acid fluorides,including addition in the presence of fluoride ions tohexafluoropropylene oxide.

This invention is now illustrated by the following examples.

Preparation of PDD

PDD was prepared in several runs by dehydrochlorination ofperfluoro-2,2-dimethyl-4,5-dichloro-1,3-dioxolane with magnesiumturnings in the presence of mercuric chloride and iodine. The additionof mercuric chloride was an improvement over Example 2 of U.S. Pat. No.3,978,030 to Resnick. As in that example, tetrahydrofuran was used asthe reaction solvent. The amount of tetrahydrofuran was 80 cm³ (about71g) per 18.9 g of the dioxolane. The amounts of the other ingredientswere as follows: magnesium 7.3 g, mercuric chloride 0.2 g, and iodine0.1 g. In each run about 15 cm³ of crude product distilling betweenabout 33° and 66° C. was collected. This consisted mainly oftetrahydrofuran and a smaller proportion of PDD.

Oligomerization of PDD

(A) The distillates of two runs were combined, mixed with 50 cm³ ofwater, and placed overnight in a refrigerator at about 0° C. The PDD,which settled to the bottom, was separated, mixed with 25 cm³ of water,and returned to the refrigerator. This water extraction process toremove the tetrahydrofuran was carried out twice more during a course oftwo months. The organic material was stored for 3 months at -5° C. andthen was distilled. The distillate was unchanged PDD, boiling at about33° C., but a high boiling heel remained. It was identified by infraredand nuclear magnetic resonance spectroscopy and by gas chromatography tobe a mixture of PDD oligomers.

(B) The preparation of PDD oligomers was repeated by keeping aPDD-tetrahydrofuran-water mixture at temperatures varying from -5° to66° C. for periods of days or hours (the reaction requiring less time athigher temperatures). The degree of PDD conversion into oligomers wasabout 20%. The recurring PDD structure was confirmed by nuclear magneticresonance spectroscopy. This technique also indicated the presence of CHbonds in the molecule.

The average degree of oligomerization of liquid products was about 4(n=4), as determined by nuclear magnetic resonance. Occasionally, veryviscous or even waxy solid products were obtained. Their degree ofoligomerization, n, was at least about 6.

(C) A small bottle was charged with 4 g of PDD, 5 g of diethyl ether,and 0.01 g of bis(4-t-butylcyclohexyl) peroxydicarbonate and allowed tostand at room temperature for one week. Evaporation of the ether left aclear, colorless, oily residue. Its infrared spectrum was consistentwith that of an oligomer having recurring PDD units joined through C-Fbonds. The spectrum also had bands characteristic of C-H bonds inradicals arising from diethyl ether. A portion of the oligomericmaterial was soluble in diethyl ether.

(D) A solution of 4 g of PDD and 0.01 g bis(4-t-butylcyclohexyl)peroxydicarbonate in 5 g of tetrahydrofuran was allowed to stand at roomtemperature for one week. Evaporation of tetrahydrofuran left a clear,colorless oil. The infrared spectrum of this oil contained bandsconsistent with the recurring PDD structure as well as some bands thatcould be attributed to C-H end groups.

FLUORINATION OF PPD OLIGOMER--PREPARATION OF OLIGOMERIC CARBOXYLIC ACID

An oligomer mixture, 2.4 g (from the reaction of PDD andtetrahydrofuran) and 50 g of 1,1,2-trichloro-1,2,2-trifluoroethane werecharged into a 350 cm³ shaker tube which was cooled, evacuated, andpressured at -30° C. to 1.19 MPa with a mixture of 25 vol. % of fluorineand 75 vol. % of nitrogen. The tube was agitated, gradually heated to180° C. over a four hour period, and then cooled.

The resulting solution was mixed well with a solution of 6 g ofpotassium carbonate in 20 cm³ of water. The organic phase was separatedfrom the water layer, and the solvent was distilled off leaving behindsolid, white potassium salts of the oligomeric carboxylic acids.Identification of the salts was by the relatively intense infraredabsorbance in the region of 5.9 μm (--COO⁻) and the similarity of theother parts of the IR scan to the absorption of the original PDDoligomer, especially the strong bands in the regions of 7.6, 8.0, 8.7,9.1, 10.1 and 13.8 μm; bands attributable to carbon-hydrogen bonds wereabsent. Elemental analysis gave C, 22.41, 22.16 and F, 52.29, 52.23%,which is consistent with a PDD oligomer having four dioxolane rings andterminated by two -COOK groups, one at each end.

The water solution, which upon standing had gelled, was made stronglyacidic by the addition of hydrochloric acid. The aqueous solution wasthen extracted with 1,1,2-trichloro-1,2,2-trifluoroethane; evaporationof the solvent gave the liquid carboxylic acids which were identified byinfrared absorbance spectroscopy. The scan showed strong absorbancies inthe regions of 3.2 μm (--OH) and 5.6 μm (CO), corresponding to those ofcarboxylic acids, as well as absorbancies attributable to the PDD rings.NMR analysis showed that the average oligomeric carboxylic acidcontained 4 recurring PDD units. Since the fluorination cleaves theoligomer at the ether sites the average oligomer prior to fluorinationcontained at least 4 PDD units.

FLUORINATION OF PPD OLIGOMER--PREPARATION OF OLIGOMERIC ACID FLUORIDES

A PDD oligomeric mixture, 2.4 g, and 50 g of1,1,2-trichloro-1,2,2-trifluoroethane were charged into a 350 mlstainless steel shaker tube; the tube was cooled, evacuated and chargedat -25° C. with a mixture of 25 vol. % fluorine and 75 vol. % nitrogenat a pressure of 1.16 MPa. The tube was agitated and slowly warmed toroom temperature and finally heated to 180° C. After cooling, thesolution was discharged from the tube and the solvent was distilled off,leaving 2.0 g of liquid acid fluorides. The oligomeric acid fluorideswere identified by their infrared absorption peak in the region of 5.3μm in addition to the typical PDD oligomer absorbancies. During thehandling of the acid fluoride some hydrolysis occurred, resulting in theformation of some carboxylic acid groups as evidenced by absorbance inthe region of 5.6 μm.

I claim:
 1. An oligomer of perfluoro(2,2-dimethyl-1,3-dioxide)containing at least one chain having the following formula: ##STR6##where k is 1 to about 4, and at least one of R and R₁ is thefluorocarbonyl group, while the other one of R and R₁ may also behydrogen.